Heat the oven to 400F. Lightly oil sheet pan and place in the oven to heat. Place the bones on the sheet pan and roast for 30 minutes, turning occasionally. Paint the bones with a thin layer of the thinned tomato paste, and roast for an additional 30 minutes, turning occasionally, until evenly browned.
Place the bones in the stockpot and cover with cold water. Bring to a boil, and then lower to a simmer. Skim any scum that forms on the surface gradually as needed.
Drain and reserve the fat from the pan; deglaze the pan with water and add to the stockpot. Continue to simmer the stock for 6-7 hours, skimming as needed. If necessary, you may add more hot water to keep the bones covered.
Toss the mirepoix (onions, carrots, celery) with the fat and brown in the oven. Add the browned mirepoix, tomatoes and sachet (parsley, thyme, bay, cloves, peppercorns, garlic placed into a 4" square of cheesecloth and tied into a sack) to the pot. Simmer for another 1-2 hours.
Strain the stock through a china cap layered with cheesecloth, and cool the stockpot in an ice-water bath. Transfer to a container and refrigerate overnight; the next day, skim off all the fat that's risen to the surface.